Recent advances in telephone communications have seen the replacement of conventional copper wire bundles by higher bandwidth and less cumbersome fiber optic transmission networks. These fiber optic networks are employed for conveying high density, high data rate signal traffic over plural fiber optic channels between geographically separated central offices. Interposed in the fiber optic links between the central offices there are usually provided a plurality of repeater stations at which the signals being conveyed over the fiber optic cables are regenerated. An example of a regenerator that may be so employed is described in the U.S. Pat. to Maione, et al, No. 4,019,048. As described in the patent, the regenerator unit contains receiver, synchronizer and transmitter circuits connected in series between an incoming optical signal fiber and an outgoing optical signal fiber. Thus, for some number N of optical communication channels (each have two fiber links, one for signal transmission in a first direction, the other for signal transmission in the opposite direction), there will be a total of 2 N fiber links, requiring 2 N repeater or regenerator units at each equipment site. The fiber optic channels themselves usually contain a group of normally active channels and one or more auxiliary or protection channels to be substituted in place of a normally active channel in the event of a failure.
Such a repeatered, multichannel environment is often augmented or served by an auxiliary monitor and control subsystem that carries out housekeeping chores with respect to the transceiver and regenerator equipment disposed along the communication lines. This auxiliary equipment, or orderwire, as it is commonly termed, operates independently of the principal transmission section of the network, so that an interruption or degradation of service over the data-conveying links will not impair the operation of the control and maintenance functions of the supervisory equipment.